H2Bub1 regulates RbohD-dependent H2O2 signal pathway in the defense responses to Verticillium dahliae toxins.

Histone H2B monoubiquitination (H2Bub1) plays critical roles in regulating growth and development as well as stress responses in Arabidopsis (Arabidopsis thaliana). In this study, we used wild-type and HUB1 and HUB2 loss-of-function Arabidopsis plants to elucidate the mechanisms involved in the regulation of the plant's defense responses to Verticillium dahliae toxins (Vd-toxins). We demonstrated that HUB-mediated H2Bub1 regulates the expression of NADPH oxidase RbohD by enhancing the enrichment of histone H3 tri-methylated on K4 in response to Vd-toxins. RbohD-dependent hydrogen peroxide (H2O2) signaling is a critical modulator in the defense response against Vd-toxins. Moreover, H2Bub1 also affects posttranscriptional mitogen-activated protein kinase (MAPK, or MPK) signaling. H2Bub1 was required for the activation of MPK3 and MPK6. MPK3 and MPK6 are involved in regulating RbohD-mediated H2O2 production. MPK3 and MPK6 are associated with protein Tyr phosphatases (PTPs), such as Tyr-specific phosphatase 1 and mitogen-activated protein kinases phosphatase 1, which negatively regulated H2O2 production. In addition, H2Bub1 is involved in regulating the expression of WRKY33. WRKY33 directly binds to RbohD and functions as a transcription factor to regulate the expression of RbohD. Collectively, our results indicate that H2Bub1 regulates NADPH oxidase RbohD-dependent H2O2 production, and the PTPs-MPK3/6-WRKY pathway plays an important role in the regulation of RbohD-dependent H2O2 signaling in defense responses to Vd-toxins in Arabidopsis.